RTL Problems / Level 2 · Sequential Logic
What You Will Learn
By solving D Flip-Flop with Synchronous Reset — Clocked Reset, you will acquire core industry skills:
- Synthesizable hardware modeling in standard Verilog-2001 / SystemVerilog.
- Correct handling of interface port contracts, edge-triggered clocks, and active-low/high resets.
- Simulation waveform interpretation and debugging using timing diagrams (VCD traces).
- Architectural avoidance of timing violations, glitching hazards, and synthesis warnings.
Problem Statement & Requirements
Implement a D flip-flop with active-high synchronous reset (sync_rst). The reset takes effect only on the rising clock edge.
Hardware design teams at leading semiconductor firms evaluate these exact port contracts, race-condition assertions, and corner cases during technical design reviews and ASIC engineer interviews.
Prerequisites: Sequential logic, clocking, synchronous control inputs.
Port List & Interface Timing
The hidden testbench instantiates top_module. Module port names and bit-widths must match the interface contract exactly:
| Name | Dir | Width | Description |
|---|---|---|---|
clk | input | 1 | Master positive-edge clock |
sync_rst | input | 1 | Active-high synchronous reset |
d | input | 1 | Data input |
q | output | 1 | Registered output |
Timing Constraints & Synthesizable RTL Rules
Timing Contract: Reset condition evaluated strictly on rising edge of `clk`. Glitches on reset between clock edges are filtered out.
Synthesis Constraints: Sensitivity list must contain ONLY `posedge clk`.
Architectural Deep Dive & Implementation Walkthrough
Common RTL Designer Pitfalls
['Accidentally placing `sync_rst` in the `always` sensitivity list, turning it into an asynchronous reset.', 'Resetting registers without meeting setup time to `clk` during synchronous reset release.']
Silicon & Hardware Engineering Notes
Synchronous reset ensures 100% synchronous timing closure and eliminates reset recovery/removal checks. However, resetting a block requires the clock to be running.
Starter RTL Code
module top_module(
input clk,
input sync_rst,
input d,
output reg q
);
// Synchronous reset DFF
endmodule
Verified Reference Solution
🔒 Reveal Verified Reference RTL Solution
module top_module(
input clk,
input sync_rst,
input d,
output reg q
);
always @(posedge clk) begin
if (sync_rst)
q <= 1'b0;
else
q <= d;
end
endmodule
Related RTL Problems in Level 2
- D Flip-Flop — Positive-Edge-Triggered Storage — Implement a basic 1-bit positive-edge-triggered D flip-flop without reset.
- D Flip-Flop with Asynchronous Reset — Reset Behavior — Design a D flip-flop with active-low asynchronous reset (areset_n). Reset forces q to 0 immediately, independent of clk.
- D Flip-Flop with Enable — Conditional Register Update — Design a D flip-flop with active-high synchronous enable (en) and active-low asynchronous reset (areset_n).
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Frequently Asked Questions
What does D Flip-Flop with Synchronous Reset — Clocked Reset require?
Implement a D flip-flop with active-high synchronous reset (sync_rst). The reset takes effect only on the rising clock edge. Implement it as Verilog module top_module matching the listed ports.
Is this design combinational or sequential?
Tags: sequential, fsm, counters, medium, flip-flops-&-latches. If a clock signal is present in the port table, implement it as sequential logic; otherwise, use continuous assignments or combinational blocks.
How is my solution graded?
A hidden SystemVerilog testbench simulates your module in the cloud judge. You pass when all directed corner cases match the golden model and the VCD timing waveform matches the contract.
How does this challenge help with semiconductor interviews?
Technical interviewers at NVIDIA, Qualcomm, Apple, and Intel routinely ask candidates to code, debug, and explain the timing waveforms of D Flip-Flop with Synchronous Reset — Clocked Reset to assess real-world synthesizability and race-condition awareness.